Jet Searchers Map Pings to Narrow Drop Zone for Robot Sub

A fifth possible signal from the missing Malaysian Air (MAS) jet gives investigators another critical data point to plot where and when to launch a remote-controlled submarine to scour the Indian Ocean seabed.

The transmission heard by a sensor-equipped buoy dropped by plane was “in the vicinity” of where the Australian navy vessel Ocean Shield detected acoustic chirps deemed to be from beacons on the airliner’s black boxes, Australia’s Joint Agency Coordination Centre said today.

Pinpointing a target zone for the sub will be pivotal, according to Dukane Seacom, the U.S. maker of the pingers. Noise from the slow-moving submersible would make it difficult to hear pulses at the same time, adding urgency to the quest to settle on a location with additional sounds before the units’ batteries die and sever search crews’ only link to debris from Flight 370.

“The more dots they can put on the map in terms of signals, then they can use the readings to narrow in,” Dukane Seacom President Anish Patel said in a phone interview from Sarasota, Florida, where the company is based.

Flight 370 had a cockpit-voice and flight-data recorder in the tail of the Boeing Co. 777-200ER, each with one Dukane Seacom pinger attached. The Malaysian Airline System Bhd. jet carrying 239 people vanished en route to Beijing from Kuala Lumpur on March 8, putting the beacons at the edge — if not beyond — the 30-day projected limit of their power packs.

Sub Ready

An unmanned sub aboard the Ocean Shield, the Bluefin-21, is ready to start scanning the seafloor with sound waves once the search zone is refined, according to the JACC. Water depths in the area exceed about 4,500 meters (14,800 feet), far from any natural light from the surface.

The possible signal detected by a sonobuoy from A Royal Australian Air Force AP-3C Orion patrol plane “will require further analysis overnight, but shows potential of being from a man-made source,” retired Air Chief Marshal Angus Houston, who heads the JACC, said in a statement.

The hunt for Flight 370 is in its 33rd day, a span marked by false leads, dashed hopes and the failure to find any physical evidence of the plane. The Ocean Shield detected two signals on April 5 and two more on April 8.

In laboratory tests, batteries on the pingers have lasted as much as 42 days “at a much lower rate,” although after Day 40, the signal probably would be so weak as to not being worth the effort to find it, Dukane Seacom’s Patel said.

‘Bonus Time’

“You’d have to be right on top of it” to locate it after day 40, he said. “This is all bonus time.”

A typical battery begins to fade after 35 days and loses “meaningful output” from 38 to 40 days, Patel said. The power declines to one-eighth to one-fourth of its normal level, he said.

“I’m glad to hear they’re still picking up signals,” he said. “That means our batteries are still doing their thing.”

Pulses from the beacons may travel farther than two miles (3.2 kilometers) in “real-world” conditions compared with laboratory tests, Patel said. Underwater temperature inversion layers known as thermoclines also can bend or reflect sound waves.

“Because of the thermoclines, because of the way the ocean can channel the sound depending on currents and topology, you may get more travel,” Patel said. “A lot of different things factor into that.”

Far Apart?

Both pingers on the two black boxes may be sending signals, and they could have ended up far apart in the thousands of meters of water in the search zone, Patel said. That may explain why authorities haven’t further pinpointed where the signals are coming from.

Patel said Dukane Seacom, a unit of Hollywood, Florida-based Heico Corp., has analyzed the findings from Ocean Shield and concluded that the signals were consistent with those from the company’s pingers.

Until the sonobuoy finding, the signals detected by ship had been the chief source of optimism among investigators that they were getting close to locating debris from the Boeing 777.

On board Ocean Shield is a crew from Phoenix International Holdings Inc., the Largo, Maryland-based contractor that is operating a towed pinger locator from the U.S. Navy that is being pulled in the Australian vessel’s wake.

By passing back and forth across the area, the Ocean Shield and the pinger locator are “narrowing the probability circle of where the debris field is suspected to be,” said John Fish, a principal of Bourne, Massachusetts-based American Underwater Search & Survey Ltd.

Getting Closer

Sounds from the pingers don’t travel as far when the signal weakens, so picking up the new contacts suggests that the Ocean Shield is getting closer to the wreckage, said Fish, whose company has helped recover numerous aircraft and their black-box recorders from underwater.

The jet’s disappearance is now the longest in modern airline history, baffling authorities because contact was lost less than an hour into a routine trip as Flight 370 headed north over the Gulf of Thailand. After vanishing from radar, the wide-body craft doubled back, flew over Peninsular Malaysia and on into some of the world’s most remote waters.

While the motive behind that heading remains unknown, Flight 370 was deliberately steered south on a path ending in the Indian Ocean, Malaysian Prime Minister Najib Razak has said.